It has been reported that difluoroacetyl chloride is useful as an intermediate for pharmaceutical and agrichemical products and as a reaction reagent, particularly a reagent for the introduction of a difluoromethyl group or difluoroacetyl group into an organic compound, and can be produced by various processes.
As a production method of a carboxylic acid chloride, there is generally known a process of reacting a carboxylic acid or a salt, ester or anhydride thereof with a chlorination agent such as chlorine, phosphorous pentachloride, phosphorous trichloride, phosphoryl chloride or thionyl chloride. It has been reported that difluoroacetyl chloride can be obtained by such a similar process. In this process, however, the raw material such as difluoroacetic acid or derivative thereof is not readily available.
By contrast, there is known a process of irradiating HCFC-132a (1,1-difluoro-3,3,3-trichloroethane), together with oxygen and chlorine, by a high-pressure mercury-vapor lamp under high-temperature conditions (Patent Document 1) as a method for producing a carboxylic acid chloride without going through difluoroacetic acid as an intermediate. In this process, the raw material is a substance that may cause ozone destruction. Further, this process is performed in a photoreaction system and thus is not so suitable for long-term production.
On the other hand, a process of thermally decomposing a 1-alkoxy-1,1,2,2-tetrafluoroethane (ATFE) in the presence of a metal oxide catalyst (Patent Document 2) and a process of decomposing a 1-alkoxy-1,1,2,2-tetrafluoroethane (ATFE) in the presence of an antimony pentafluoride catalyst under low-temperature conditions (Patent Document 3) are known as production methods of difluoroacetyl fluoride (hereinafter sometimes abbreviated as “DFAC”). A process of converting a perfluorocarboxylic acid fluoride to a corresponding acid chloride by halogen exchange reaction with lithium chloride (Non-Patent Document 1) and a process of forming benzoyl chloride by reaction of benzoyl fluoride with calcium chloride (Patent Document 4) have been reported as methods for direct conversion from carboxylic acid fluorides to carboxylic acid chlorides.